The present invention relates to metallurgy and, more particularly, to the production of metallurgical compositions involving a continuous phase or matrix and a dispersed phase of dispersoid. More particularly, the present invention relates to "stable dispersoid strengthened" composite materials in which a relatively soft copper matrix provides at least one desired characteristic and a relatively hard refractory dispersoid provides at least another desired characteristic. Of all available materials, copper generally offers the best combination of lowest cost and highest electrical conductivity with adequate strength and corrosion resistance. Moreover, its strength can be greatly increased by cold-working with small reduction in electrical conductivity. In practice, cold worked commercially pure copper constitutes the optimum choice for electrical conductors, switches, etc. requiring higher strength than that of annealed copper at room temperature. On the other hand, the strengthening effect of cold-work is gradually lost by heating via atomic phenomena known as "recovery" and "recrystallization." In pure copper, these phenomena occur below the service temperatures and times increasingly desired in modern electrical machinery, i.e. higher hot creep strength is required.
In accordance with known techniques, hot strength can be obtained by solid solution hardening or precipitation hardening. With the former, as a result of there being a high concentration of alloy in the copper matrix, electrical conductivity is drastically lowered. With the latter, as temperature and/or time increase, the hardening precipitate, which was produced originally by differential temperature change, returns to solution in the metal matrix so as to lower electrical conductivity drastically. The present invention involves another technique, called stable dispersoid strengthening, which, as is well-known, involves a uniform distribution of very small particles throughout the metal matrix. These particles are "stable" in that they essentially are insoluble in both the solid and the molten metal and, hence, have only a limited tendency to reduce electrical conductivity by solid solution. But these particles are sufficiently small and numerous to block effectively the atomic rearrangements that constitute recovery and recrystallization. As a result, these particles maintain the desirable strain hardening of cold work or the like (desirable because of strengthening plus minimum effect on electrical conductivity) from room temperature to well above the recovery and recrystallization temperatures of the copper matrix. Stable dispersoid strengthening of the foregoing type can be achieved in various ways, including; fusion meallurgy by which the dispersoid particles are mixed into a matrix melt; powder metallurgy by which dispersoid particles and soft matrix particles are mixed and compacted; or by internal reaction involving precipitation of dispersoid particles in a matrix melt by chemical reaction. The present invention is based on the discovery of novel internal reaction techniques by which particles having an unusual combination of refractory properties and selected size can be maintained as a dispersion within a copper matrix during solidification.